Being anti-union doesn't mean favoring slave labor or breaking laws. Many rights of workers are protected by legislation (depending where in the world you live), and unionism doesn't mean higher wages.
For those of us whom are not American, there is a similar day strangely called Labour Day, which is celebrated world wide for similar reasons, Small world hey :)
But in context what the unions did was important, it doesn't mean that they are needed, relevant, or beneficial in current day. We celebrate Xmas, but that doesn't mean that we have a guy wearing a Santa (non-christian) uniform everyday.
But everyday we enjoy things like child labor laws, paid time off, safe working conditions, limits on shift-lengths, overtime pay, maternity/paternity leave, and myriad others.
How do you think those rights found their way in to the legislation, and remain there?
Look I not blind to the history, and protectionisms which came about from unionism. But that is a common retort, but also a bit of a straw man argument.
I wasn't aware I was making an argument.
Ok that makes sense now.
"Many rights of workers are protected by legislation" - sure but employees are rarely able take the case to court without union backing.
In several countries where I have lived you don't need a court for industrial conflicts, there are arbitrators, mediators, and small courts which deal with such items.
That legislation exists because of unions